# Text Interpolation

How `RJS` resolves `{{ }}` in text nodes, and which value helpers it supports.

## Resolution

`#FIT_TEXT` (top level) / `#FIT_TEXT_IN_ARRAY` / `#FIT_TEXT_IN_OBJECT` (inside `:for`) scan text nodes for `{{ ... }}` and resolve each match through `#GET_VALUE`, which supports:

## Helpers

| Helper | Behavior |
| --- | --- |
| `{{ key.path }}` | Dot-path lookup into `data`, walked layer by layer via `#GET_VALUE_FROM_LAYERS` |
| `{{ CALC(key + n) }}` | Arithmetic: `+ - * / %`, applied via `#CALC` |
| `{{ LENGTH(key) }}` | `Object.keys(value).length` for plain objects, `value.length` otherwise |
| `{{ UPPER(key) }}` / `{{ LOWER(key) }}` | `.toUpperCase()` / `.toLowerCase()` |
| `{{ DATE(key, format) }}` | Parses `key` as a Unix timestamp and formats it (see `Number.$format` in [Date and Number Extensions](/api-reference-date-time)) |

## Embedded Text

`REGEX_TEXT` also matches a value embedded inside surrounding literal text (`prefix {{ key }} suffix`), preserving the prefix/suffix when substituting.